Method and apparatus for discovering communication entity

ABSTRACT

Disclosed herein are an apparatus and method for discovering a communication entity. The apparatus for discovering a communication entity includes a list generation unit for generating a list of connection target Data Readers (DRs), a counter generation unit for generating a counter including information about a number of the connection target DRs, and a discovery message communication unit for establishing communication connections to the connection target DRs based on the list and the counter. The discovery message communication unit includes a transmission unit for transmitting a DR discovery message including data topic information or possible service quality information to each of the connection target DRs, and a reception unit for receiving a Data Writer (DW) discovery message including data topic information or possible service quality information from each of the connection target DRs.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2013-0064402 filed on Jun. 5, 2013, which is hereby incorporated byreference in its entirety into this application.

BACKGROUND

1. Field

The present invention relates generally to a method and apparatus fordiscovering a communication entity and, more particularly, to a methodand apparatus for discovering a communication entity, which can provideefficient and reliable communication between communication nodesrequiring interaction in a complex system composed of large-scalephysical nodes.

2. Description of Related Art

When communication entities that are targets to be connected aredirectly recognized and connection information thereof is managed uponestablishing a communication connection, a communication connectionneeds only to be directly established based on connection information ifinteraction is required. However, as the number of communicationentities constituting the entire application domain has rapidlyincreased, the number of data types to be exchanged and the number ofservices to be provided has also rapidly increased. Accordingly, it isdifficult for individual nodes to manage such data types and services onthe whole, and pieces of data and a number of servicesprovided/requested for respective nodes may vary depending on the statesof the nodes, thus making it realistically impossible for each node topreviously set/manage information about counterpart communicationentities to which the corresponding node is to be connected. In order toperform such a function, communication middleware has appeared, and DataDistribution Service (DDS) technology standardized by Object ManagementGroup (OMG) has been widely used based on the field of national defense.Further, in Korean Patent Application Publication No. 2008-0001144 orthe like, a method of recognizing a communication entity which willrequest/provide the corresponding data or service at the time at whichdata or service is actually required and searching for connectioninformation about the corresponding entity has been introduced. Since amethod of discovering a communication entity must find connectioninformation about a target entity in a state in which the target entityis not recognized, two types of methods are chiefly used. One is amethod of requesting information related to a communication connectionfrom unspecified communication entities constituting the entireapplication domain and receiving a response to the request in amulticasting/broadcasting manner. The other is a method of providing aserver at the center of the domain, registering data or serviceinformation to be provided/requested by the corresponding node itself onthe server, searching for the data or service information, and acquiringconnection information about a counterpart communication entity havebeen chiefly used. As in the case of the latter, when the server isplaced at the center, there is a disadvantage in that when the server isnot desirably operated, it is difficult to execute the entireapplication. In the case of the former, distributed processing ispossible, so that, even if a specific node is malfunctioning, there islittle influence exerted on the entire application, but there is adisadvantage in that, when a network to connect communication entitiesconstituting the entire application domain does not support broadcastingor multicasting, it is difficult to apply the former method.

SUMMARY

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the prior art, and an object of the presentinvention is to predefine information about communication entities towhich connections are to be made and thus to reduce the number ofmessages and the size of related loads required for discovery asdiscovery is performed for the predefined communication entities.

Another object of the present invention is to predefine informationabout time interval variable values and information about the number ofcommunication entities to which a current node is to be connected, forrespective nodes, thus preventing messages from colliding with eachother in each node.

A further object of the present invention is to utilize a discoverytechnique, provided by a Data Distribution Service (DDS), under aspecific condition, thus enabling a communication entity that belatedlyjoins a network to be discovered.

In accordance with an aspect of the present invention to accomplish theabove objects, there is provided a method for discovering acommunication entity, including generating a list of connection targetData Readers (DRs); generating a counter including information about anumber of the connection target DRs; and establishing communicationconnections to the connection target DRs based on the list and thecounter, wherein establishing the communication connections comprisestransmitting a DR discovery message including data topic information orpossible service quality information to each of the connection targetDRs, and receiving a Data Writer (DW) discovery message including datatopic information or possible service quality information from each ofthe connection target DRs.

Preferably, the method may further include generating time informationincluding information about a transmission time interval required toprevent individual DR discovery messages from colliding with each otherand a waiting time required to receive the DW discovery message, whereintransmitting is performed based on the list, the counter, and the timeinformation.

Preferably, the method may further include, after establishing thecommunication connections, determining, based on the counter, whetherconnections to a number of connection target DRs corresponding to thenumber of connection target DRs, included in the counter, have beencompleted.

Preferably, determining may further include, if the connections have notbeen completed even after the waiting time, transmitting a DomainParticipant (DP) discovery message required to discover a DP that is acontainer object for managing communication entities using a one-to-manycommunication method.

Preferably, transmitting the DR discovery message may be performed ateach transmission time interval until the DR discovery message istransmitted to a last connection target DR in the list.

Preferably, if the DR discovery message has been transmitted to a lastconnection target DR in the list, a current state may be changed to awaiting state for receiving a DW discovery message from a DR that is notpresent in the list.

Preferably, when the current state is changed to the waiting state, acommunication connection to the DR may be established by transmitting aDR discovery message to the DR after the DW discovery message has beenreceived.

Preferably, transmitting the DP discovery message may be performed ateach preset transmission time interval.

Preferably, establishing may be configured to, if information includedin the DR discovery message is information corresponding to a topic anda service quality of a corresponding connection target DR, receive a DWdiscovery message from the connection target DR.

Preferably, if the DR discovery message is transmitted as a response tothe DW discovery message, a current state may be changed to a waitingstate for receiving a DW discovery message from a DR that is not presentin the list.

In accordance with another aspect of the present invention to accomplishthe above objects, there is provided an apparatus for discovering acommunication entity, including a list generation unit for generating alist of connection target Data Readers (DRs); a counter generation unitfor generating a counter including information about a number of theconnection target DRs; and a discovery message communication unit forestablishing communication connections to the connection target DRsbased on the list and the counter, wherein the discovery messagecommunication unit comprises a transmission unit for transmitting a DRdiscovery message including data topic information or possible servicequality information to each of the connection target DRs, and areception unit for receiving a Data Writer (DW) discovery messageincluding data topic information or possible service quality informationfrom each of the connection target DRs.

Preferably, the apparatus may further include a time informationgeneration unit for generating time information including informationabout a transmission time interval required to prevent individual DRdiscovery messages from colliding with each other and a waiting timerequired to receive the DW discovery message, wherein the discoverymessage communication unit establishes the communication connections tothe connection target DRs based on the list, the counter, and the timeinformation.

Preferably, the discovery message communication unit may further includea determination unit for determining, based on the counter, whetherconnections to a number of connection target DRs corresponding to thenumber of connection target DRs, included in the counter, have beencompleted.

Preferably, the transmission unit may be configured to, if it isdetermined that the connections have not been completed even after thewaiting time, transmit a Domain Participant (DP) discovery messagerequired to discover a DP that is a container object for managingcommunication entities using a one-to-many communication method.

Preferably, the transmission unit may transmit the DR discovery messageat each transmission time interval until the DR discovery message istransmitted to a last connection target DR in the list.

Preferably, the discovery message communication unit may be configuredto, if the DR discovery message has been transmitted to a lastconnection target DR in the list, change a current state to a waitingstate for receiving a DW discovery message from a DR that is not presentin the list.

Preferably, the discovery message communication unit may be configuredto, when the current state is changed to the waiting state, establish acommunication connection to the DR by transmitting a DR discoverymessage to the DR after the DW discovery message has been received fromthe DR.

Preferably, the transmission unit may transmit the DP discovery messageat each preset transmission time interval.

Preferably, the reception unit may be configured to, if informationincluded in the DR discovery message is information corresponding to atopic and a service quality of a corresponding connection target DR,receive a DW discovery message from the connection target DR.

Preferably, the discovery message communication unit may be configuredto, if the DR discovery message is transmitted as a response to the DWdiscovery message, change a current state to a waiting state forreceiving a DW discovery message from a DR that is not present in thelist.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagram showing the basic structure of Data DistributionService (DDS) middleware;

FIG. 2 is a diagram showing a conceptual procedure in which the DDSmiddleware discovers a communication entity;

FIGS. 3 and 4 are flowcharts showing a method for discovering acommunication entity according to the present invention;

FIG. 5 is a diagram showing an embodiment of a communication entitydiscovery method according to the present invention; and

FIG. 6 is a block diagram showing an apparatus for discovering acommunication entity according to the present invention.

DETAILED DESCRIPTION

The present invention will be described in detail below with referenceto the accompanying drawings. Repeated descriptions and descriptions ofknown functions and configurations which have been deemed to make thegist of the present invention unnecessarily obscure will be omittedbelow. The embodiments of the present invention are intended to fullydescribe the present invention to a person having ordinary knowledge inthe art to which the present invention pertains. Accordingly, theshapes, sizes, etc. of components in the drawings may be exaggerated tomake the description clearer.

Hereinafter, the basic structure of Data Distribution Service (DDS)middleware and a conceptual procedure for discovering a communicationentity will be described. FIG. 1 is a diagram showing the basicstructure of DDS middleware, and FIG. 2 is a diagram showing aconceptual procedure in which the DDS middleware discovers acommunication entity.

Referring to FIGS. 1 and 2, DDS middleware includes a Data Writer (DW)100 for transmitting data and a Data Reader (DR) 200 for receiving dataas communication entities 1 a and 2 a which will actually exchange datafor each data topic defined by an application. As a container entity formanaging the communication entities, a Domain Participant (DP) 300 ispresent. Unless an additional application using DDS is present in thecorresponding node, a single DP 300 is present per node. The structureof a network in which DDS is operated basically premises the environmentof a single network 400 in which transmission media are shared.Therefore, discovery for communication in DDS is divided into a primarystage in which DPs present in respective nodes are mutually found, and asecondary stage in which a communication entity taking charge oftransmission of data topics desired to be exchanged by the correspondingnode is discovered for each found DP. Since a DP does not recognizewhich nodes are present in the network, a data transmission node 1 orreception node 2 notifies the network of the presence of DP using agroup communication method 10 such as multicasting or broadcasting ifits own DP is generated, thus completing the discovery of other DPspresent in a DDS domain. Thereafter, each node performs secondarydiscovery using a unicasting method 20 to determine whether acommunication entity 1 a or 2 a related to its own data topic is presentin the discovered remaining DPs. In the secondary discovery stage, whena counterpart node has a communication entity related to a currentnode's data topic, the communication entity of the current nodeestablishes a communication connection to the communication entity, anddata exchange 30 is performed between the two communication entities.

When the above method defined in DDS is used, a primary discovery stageis configured such that, if the number of nodes exceeds a predeterminednumber, and individual nodes simultaneously transmit discovery messagesusing a multicasting or broadcasting method as in the case of a complexsystem in which nodes are closely coupled to each other, a networkenvironment in which transmission media are shared causes an overload ona network and then makes it impossible to exchange the discoverymessages. Further, the secondary discovery stage is disadvantageous inthat, after nodes have been discovered, communication entities relatedto a data topic required by the current node are discovered in all ofthe discovered nodes, and thus the number of messages and the size ofrelated loads required for discovery are increased. In order to solvethis disadvantage, the present invention presents a scheme forpredefining information about communication entities to whichconnections are to be made and basically performing mutual discoverybased on the predefined information. Further, in order to preventmessages from colliding with each other in each node, information abouttime interval variable values and information about the number ofcommunication entities to which a current node is to be connected aremaintained and utilized for respective nodes. Furthermore, a discoverytechnique provided by DDS is utilized some conditions, and thuscommunication entities belatedly joining a network may also bediscovered.

Hereinafter, a method of discovering a communication entity according tothe present invention will be described in detail. FIGS. 3 and 4 areflowcharts showing a communication entity discovery method according tothe present invention.

Referring to FIGS. 3 and 4, the communication entity discovery methodaccording to the present invention includes the step S10 of generating alist of connection target Data Readers (DRs), the step S20 of generatinga counter including information about the number of connection targetDRs, the step S30 of generating time information including atransmission time interval and a waiting time, and the step S40 ofestablishing communication connections to the connection target DRsbased on the list, the counter, and the time information.

In this case, the step S40 of establishing communication connections tothe connection target DRs includes the step S41 of transmitting a DRdiscovery message including data topic information or possible servicequality information to the connection target DRs, and the step S42 ofreceiving a Data Writer (DW) discovery message including data topicinformation or possible service quality information from the connectiontarget DRs.

At the step S10 of generating the list of connection target DRs, thelist includes information about other communication entities to which acurrent node itself must establish connections. At the step S20 ofgenerating the counter including information about the number ofconnection target DRs, the counter includes information about the totalnumber of communication entities to which the current node is to beconnected. At the step S30 of generating the time information includingthe transmission time interval and the waiting time, the timeinformation denotes information required to determine a time intervaland a basic waiting time which are to be applied between discoverymessages when multiple discovery messages are transmitted by each node,wherein such time information may be defined as different values forrespective nodes. Each node sets such a time interval value to a maximumvalue, selects a random value within this time interval for eachmessage, and transmits a message so that a time difference with aprevious message is maintained by the random value. This results in anadvantage in that the occurrence of a collision between messages isminimized when multiple nodes simultaneously transmit discovery messagesfor respective nodes. The step of establishing communication connectionsto communication target DRs based on the list, the counter, and the timeinformation will be described in detail later.

Hereinafter, embodiments of a method and apparatus for discovering acommunication entity according to the present invention will bedescribed in detail. FIG. 5 is a diagram showing an embodiment of amethod for discovering a communication entity according to the presentinvention.

Referring to FIG. 5, a communication entity discovery apparatus 100according to the present invention, and DR1 210, DR2 220, DR3 230, andDR4 240, as Data Readers (DRs) to which the communication entitydiscovery apparatus is to be connected, are present. In this case, it ispremised that the DR1 210, DR2 220, and DR3 230 are stored as connectiontarget DRs in the list of the communication entity discovery apparatus100. Further, it is premised that the total number of DRs to which theapparatus is to be connected is defined as four in the counter of thecommunication entity discovery apparatus 100.

The communication entity discovery apparatus 100 checks informationabout the characteristics of and the total number of DRs to which it isto be connected, based on the list and counter thereof. Thereafter, thecommunication entity discovery apparatus 100 transmits a DR discoverymessage including data topic information or possible service qualityinformation to the DR1 210 corresponding to a connection target DR atstep S110. In this case, the DR1 210 being in a waiting state receivesthe DR discovery message, and determines whether the topic informationof the DR discovery message is identical to its own data topic, orwhether the service quality of the DR discovery message satisfies itsown desired service quality. As a result of the determination, if theabove requirement has been fulfilled, the DR1 210 transmits a DataWriter (DW) discovery message including its own data topic informationor possible service quality information to the communication entitydiscovery apparatus 100 at step S120. By means of mutual transmission atsteps S110 and S120, the DR1 210 and the communication entity discoveryapparatus 100 are connected at step S130.

In this case, the communication entity discovery apparatus 100 checksits own list at step S140, and determines whether a DR discovery messagehas been transmitted to the last connection target DR in the list. Inthis case, if it is determined that the DR discovery message has notbeen transmitted to the last connection target, the communication entitydiscovery apparatus 100 transmits a DR discovery message to the DR2 220corresponding to a next DR in the list at step S150. In this case, theDR2 220 being in a waiting state receives the DR discovery message, anddetermines whether the data topic information of the DR discoverymessage is identical to its own data topic or whether the servicequality of the DR discovery message satisfies its own desired servicequality. If it is determined that the requirement has been fulfilled,the DR2 220 transmits a DW discovery message including its own datatopic information or possible service quality information to thecommunication entity discovery apparatus 100 at step S160. By means ofmutual transmission at steps S150 and S160, the DR2 220 and thecommunication entity discovery apparatus 100 are connected at step S170.

Thereafter, the communication entity discovery apparatus 100 checks itslist at step S180, and determines whether a DR discovery message hasbeen transmitted to the last connection target DR in the list. Here, ifit is determined that the DR discovery message has not been transmittedto the last connection target, the communication entity discoveryapparatus 100 transmits a DR discovery message to the DR3 230corresponding to a next DR in the list at step S190. The DR discoverymessages transmitted to the DR1 210, DR2 220, and DR3 230 are configuredto be sent at preset transmission time intervals based on predefinedtime information. The communication entity discovery apparatus checksthe list again at step S200, and then determines that the DR discoverymessage has been transmitted to the DR3 230 corresponding to the lastconnection target. In this case, the communication entity discoveryapparatus changes its state to a waiting state so as to receive a DWdiscovery message from the DR4 240 which is not present in the list. Ifthe communication entity discovery apparatus changes its state to thewaiting state, the communication entity discovery apparatus receives aDW discovery message from the DR4 240 at step S220. Thereafter, thecommunication entity discovery apparatus transmits a DR discoverymessage to the DR4 240 at step S230, and thus establishes acommunication connection to the DR4 240. That is, the communicationentity discovery apparatus receives the DW discovery message from theDR4 before transmitting the DR discovery message, and transmits the DRdiscovery message as a response to the DW discovery message, thus makinga communication connection. Further, when the DR discovery message fromthe communication entity discovery apparatus has been transmitted as aresponse to the DW discovery message, the communication entity discoveryapparatus changes its state to a waiting state so as to receive a DWdiscovery message from a DR which is not present in the list at stepS250. In this regard, the waiting state is not continuously maintained.That is, if connections to a number of DRs corresponding to the totalnumber of DRs to be connected, which is stored in the counter, have notbeen completed even if the communication entity discovery apparatus iswaiting for the preset waiting time (S260), based on the waiting time(S260) stored in the time information, the communication entitydiscovery apparatus transmits a Domain Participant (DP) discoverymessage required to discover a DP which is a container object formanaging communication entities using a one-to-many communication methodat step S270. Continuing with FIG. 5, it is premised in the counter thatthe communication entity discovery apparatus is to be connected to fourDRs, but only three DRs, that is, DR1 210, DR2 220, and DR4 240, arecurrently connected to the apparatus. Here, the term “one-to-manycommunication” denotes a group communication method such as multicastingor broadcasting. In this case, the DP discovery message is transmittedat each transmission time interval (S280) based on the transmission timeinterval included in the time information. Therefore, if thetransmission time interval (S280) has elapsed after the performance ofstep S270, a DP discovery message is retransmitted at step S290.

Hereinafter, the configuration and operation of the communication entitydiscovery apparatus according to the present invention will be describedin detail. FIG. 6 is a block diagram showing a communication entitydiscovery apparatus according to the present invention.

Referring to FIG. 6, the communication entity discovery apparatus 100according to the present invention includes a list generation unit 110,a counter generation unit 120, a time information generation unit 140,and a discovery message communication unit 130. The list generation unit110 generates a list of connection target DRs. The counter generationunit 120 generates a counter including information about the number ofconnection target DRs. The time information generation unit 140generates time information including information about a transmissiontime interval required to prevent discovery messages from colliding witheach other and a waiting time required to receive DW discovery messages.The discovery message communication unit 130 establishes communicationconnections to the connection target DRs based on the list, the counter,and the time information. In this case, the discovery messagecommunication unit 130 includes a transmission unit 131 for transmittinga DR discovery message including data topic information or possibleservice quality information to the connection target DRs, and areception unit 132 for receiving a DW discovery message including datatopic information or possible service quality information from theconnection target DRs.

Further, the discovery message communication unit 130 may furtherinclude a determination unit 133 for determining whether connections toa number of connection target DRs corresponding to the number ofconnection target DRs, stored in the counter, have been completed.

The list generated by the list generation unit 110 includes informationabout other communication entities to which the apparatus must establishconnections. The counter generated by the counter generation unit 120includes information about the total number of communication entities towhich the apparatus is to be connected. The time information generatedby the time information generation unit 140 denotes information requiredto determine a time interval and a basic waiting time to be appliedbetween discovery messages when each node transmits a plurality ofdiscovery messages, and such information may be defined as differentvalues for respective nodes. Each node sets such a time interval valueto a maximum value, selects a random value within this time interval foreach message, and transmits a message so that a time difference with aprevious message is maintained by the random value. This results in anadvantage in that the occurrence of a collision between messages isminimized when multiple nodes simultaneously transmit discovery messagesfor respective nodes.

The communication entity discovery apparatus 100 checks informationabout the characteristics of and the total number of DRs to which it isto be connected, based on its list and counter. Thereafter, thecommunication entity discovery apparatus 100 transmits a DR discoverymessage including data topic information or possible service qualityinformation to the DR1 corresponding to a connection target DR. In thiscase, the DR1 being in a waiting state receives the DR discoverymessage, and determines whether the topic information of the DRdiscovery message is identical to its own data topic, or whether theservice quality of the DR discovery message satisfies its own desiredservice quality. As a result of the determination, if the aboverequirement has been fulfilled, the DR1 transmits a Data Writer (DW)discovery message including its own data topic information or possibleservice quality information to the communication entity discoveryapparatus 100. Therefore, the DR1 and the communication entity discoveryapparatus 100 are connected.

In this case, the communication entity discovery apparatus 100 checksits own list, and determines whether a DR discovery message has beentransmitted to the last connection target DR in the list. In this case,if it is determined that the DR discovery message has not beentransmitted to the last connection target, the communication entitydiscovery apparatus 100 transmits a DR discovery message to the DR2corresponding to a next DR in the list. In this case, the DR2 being in awaiting state receives the DR discovery message, and determines whetherthe data topic information of the DR discovery message is identical toits own data topic or whether the service quality of the DR discoverymessage satisfies its own desired service quality. If it is determinedthat the requirement has been fulfilled, the DR2 transmits a DWdiscovery message including its own data topic information or possibleservice quality information to the communication entity discoveryapparatus 100. Therefore, the DR2 and the communication entity discoveryapparatus 100 are connected.

The communication entity discovery apparatus 100 checks its list, anddetermines whether a DR discovery message has been transmitted to thelast connection target DR in the list. Here, if it is determined thatthe DR discovery message has not been transmitted to the last connectiontarget, the communication entity discovery apparatus 100 transmits a DRdiscovery message to a DR corresponding to a next DR in the list. Inthis case, the DR discovery message is transmitted at each presettransmission time interval based on predefined time information. Thecommunication entity discovery apparatus 100 checks the list again. Ifit is determined that the DR discovery message has been transmitted to aDR corresponding to the last connection target, the communication entitydiscovery apparatus 100 changes its state to a waiting state so as toreceive a DW discovery message from a non-present DR which is notpresent in the list. If the communication entity discovery apparatuschanges its state to the waiting state, the communication entitydiscovery apparatus receives a DW discovery message from the non-presentDR, transmits a DR discovery message to the non-present DR, and thenestablishes a communication connection to the non-present DR. That is,the communication entity discovery apparatus receives the DW discoverymessage from the non-present DR before transmitting the DR discoverymessage, and transmits the DR discovery message as a response to the DWdiscovery message, thus making a communication connection. Further, evenwhen the DR discovery message from the communication entity discoveryapparatus has been transmitted as a response to the DW discoverymessage, the communication entity discovery apparatus changes its stateto a waiting state so as to receive a DW discovery message from anon-present DR which is not present in the list. In this regard, thewaiting state is not continuously maintained. That is, if connections toa number of DRs corresponding to the total number of DRs to beconnected, which is stored in the counter, have not been completed evenif the communication entity discovery apparatus is waiting for thepreset waiting time, based on the waiting time stored in the timeinformation, the communication entity discovery apparatus transmits aDomain Participant (DP) discovery message required to discover a DPwhich is a container object for managing communication entities using aone-to-many communication method. Here, the term “one-to-manycommunication” denotes a group communication method such as multicastingor broadcasting. In this case, the DP discovery message is transmittedat each transmission time interval based on the transmission timeinterval included in the time information.

In accordance with the present invention, information aboutcommunication entities to which connections are to be made ispredefined, thus reducing the number of messages and the size of relatedloads required for discovery as discovery is performed for thepredefined communication entities.

Further, in accordance with the present invention, information abouttime interval variable values and information about the number ofcommunication entities to which a current node is to be connected arepredefined for respective nodes, thus preventing messages from collidingwith each other in each node.

Furthermore, in accordance with the present invention, a discoverytechnique, provided by a Data Distribution Service (DDS), is utilizedunder a specific condition, thus enabling a communication entity thatbelatedly joins a network to be discovered.

As described above, in the apparatus and method for discovering acommunication entity according to the present invention, theconfigurations and schemes in the above-described embodiments are notlimitedly applied, and some or all of the above embodiments can beselectively combined and configured so that various modifications arepossible.

What is claimed is:
 1. A method for discovering a communication entity,comprising: generating a list of connection target Data Readers (DRs);generating a counter including information about a number of theconnection target DRs; and establishing communication connections to theconnection target DRs based on the list and the counter, whereinestablishing the communication connections comprises: transmitting a DRdiscovery message including data topic information or possible servicequality information to each of the connection target DRs, and receivinga Data Writer (DW) discovery message including data topic information orpossible service quality information from each of the connection targetDRs.
 2. The method of claim 1, further comprising generating timeinformation including information about a transmission time intervalrequired to prevent individual DR discovery messages from colliding witheach other and a waiting time required to receive the DW discoverymessage, wherein transmitting is performed based on the list, thecounter, and the time information.
 3. The method of claim 2, furthercomprising, after establishing the communication connections,determining, based on the counter, whether connections to a number ofconnection target DRs corresponding to the number of connection targetDRs, included in the counter, have been completed.
 4. The method ofclaim 3, wherein determining further comprises, if the connections havenot been completed even after the waiting time, transmitting a DomainParticipant (DP) discovery message required to discover a DP that is acontainer object for managing communication entities using a one-to-manycommunication method.
 5. The method of claim 2, wherein transmitting theDR discovery message is performed at each transmission time intervaluntil the DR discovery message is transmitted to a last connectiontarget DR in the list.
 6. The method of claim 2, wherein if the DRdiscovery message has been transmitted to a last connection target DR inthe list, a current state is changed to a waiting state for receiving aDW discovery message from a DR that is not present in the list.
 7. Themethod of claim 6, wherein, when the current state is changed to thewaiting state, a communication connection to the DR is established bytransmitting a DR discovery message to the DR after the DW discoverymessage has been received.
 8. The method of claim 4, whereintransmitting the DP discovery message is performed at each presettransmission time interval.
 9. The method of claim 1, whereinestablishing is configured to, if information included in the DRdiscovery message is information corresponding to a topic and a servicequality of a corresponding connection target DR, receive a DW discoverymessage from the connection target DR.
 10. The method of claim 1,wherein if the DR discovery message is transmitted as a response to theDW discovery message, a current state is changed to a waiting state forreceiving a DW discovery message from a DR that is not present in thelist.
 11. An apparatus for discovering a communication entity,comprising: a list generation unit configured to generate a list ofconnection target Data Readers (DRs); a counter generation unitconfigured to generate a counter including information about a number ofthe connection target DRs; and a discovery message communication unitconfigured to establish communication connections to the connectiontarget DRs based on the list and the counter, wherein the discoverymessage communication unit comprises: a transmission unit configured totransmit a DR discovery message including data topic information orpossible service quality information to each of the connection targetDRs, and a reception unit configured to receive a Data Writer (DW)discovery message including data topic information or possible servicequality information from each of the connection target DRs.
 12. Theapparatus of claim 11, further comprising a time information generationunit configured to generate time information including information abouta transmission time interval required to prevent individual DR discoverymessages from colliding with each other and a waiting time required toreceive the DW discovery message, wherein the discovery messagecommunication unit establishes the communication connections to theconnection target DRs based on the list, the counter, and the timeinformation.
 13. The apparatus of claim 12, wherein the discoverymessage communication unit further comprises a determination unitconfigured to determine, based on the counter, whether connections to anumber of connection target DRs corresponding to the number ofconnection target DRs, included in the counter, have been completed. 14.The apparatus of claim 13, wherein the transmission unit is configuredto, if it is determined that the connections have not been completedeven after the waiting time, transmit a Domain Participant (DP)discovery message required to discover a DP that is a container objectfor managing communication entities using a one-to-many communicationmethod.
 15. The apparatus of claim 12, wherein the transmission unittransmits the DR discovery message at each transmission time intervaluntil the DR discovery message is transmitted to a last connectiontarget DR in the list.
 16. The apparatus of claim 12, wherein thediscovery message communication unit is configured to, if the DRdiscovery message has been transmitted to a last connection target DR inthe list, change a current state to a waiting state for receiving a DWdiscovery message from a DR that is not present in the list.
 17. Theapparatus of claim 16, wherein the discovery message communication unitis configured to, when the current state is changed to the waitingstate, establish a communication connection to the DR by transmitting aDR discovery message to the DR after the DW discovery message has beenreceived from the DR.
 18. The apparatus of claim 14, wherein thetransmission unit transmits the DP discovery message at each presettransmission time interval.
 19. The apparatus of claim 11, wherein thereception unit is configured to, if information included in the DRdiscovery message is information corresponding to a topic and a servicequality of a corresponding connection target DR, receive a DW discoverymessage from the connection target DR.
 20. The apparatus of claim 11,wherein the discovery message communication unit is configured to, ifthe DR discovery message is transmitted as a response to the DWdiscovery message, change a current state to a waiting state forreceiving a DW discovery message from a DR that is not present in thelist.